With reference to FIG. 1, a known LED traffic signal 10 includes a housing 12, a printed circuit board 14 disposed in the housing, a plurality of LEDs 16 mounted on the printed circuit board, a lens 18, and a light-transmissive cover 20 that also connects to the housing. A gasket 24 can be provided to press against the light transmissive cover 20 and the housing 12 to protect the internal electrical components. The printed circuit board 14 receives electrical power through wires 26 connected to a plug-in socket 28 at one end and connector pins 32 at the other end. An electrical component 36 is provided on the printed circuit board 14 to condition the power that is received from the electrical power source.
LED signals attempt to collimate light to direct the light generated by the LEDs 16 towards the viewer of the signal. A schematic depiction of a portion of the lens 18 interacting with a respective LED 16 is shown in FIG. 2. In FIG. 2, the LED 16 is shown as a point light source that interacts with a portion of the collimating lens 18. Light rays 40 emitted from the LED enter the lens 18 at an inner surface 42 and are directed towards an outer surface 44 where they refract to generate a collimated light beam pattern.
LED signal lamps that employ a collimating lens are especially susceptible to the “sun phantom” effect because the most surfaces the LED package are highly reflective. With reference to FIG. 2, parallel light from the sun that impinges upon the outer surface 44 of the lens 18 is directed back towards the LED 16 since the incoming light rays follow the same path as the light rays 40 emanating from the LED. The incoming sunlight reflects off of the internal reflector of the LED package 16 back towards the lens 18. Since the internal reflector is so highly reflective, the reflected light can make the signal appear “on” to one viewing the signal.
Previous attempts to control the “sun phantom” effect in LED signals have employed the use of a large radius spherical outer distribution cover which is angled to reflect stray light away from the viewer towards the ground.